1. Field of the Invention
This invention relates to an improvement of the so-called retainer type lead acid battery wherein a capacity of a negative plate is made higher than a capacity of a positive plate and an amount of electrolyte is limited, and a method of storing it. The object of the present invention is to improve a discharge storage characteristic.
2. Description of the Prior Art
A conventional retainer type lead acid battery increases a capacity of negative plate 10 to 30% as compared with that of the positive plate and limits an amount of the electrolyte, so that firstly the positive plate is fully charged and oxygen generated at the positive plate in overcharging is absorbed and consumed at the negative plate.
However, when the battery of this kind is allowed to stand for a long period of time after being discharged a corroded layer of a positive collector surface composed of lead or lead alloy, which supports a positive active material in a positive plate, is changed to an inactive PbSO.sub.4 (lead sulfate) layer to increase a resistance between the positive active material and the positive collector. As a result, the charging efficiency is lowered and the capacity is not sufficiently recovered so as to deteriorate the battery characteristics.
Now, according to the investigation of the inventors, the mechanism by which the corroded layer of the positive collector surface is changed to the inactive PbSO.sub.4 layer after the discharge storage as described above may be considered as follows. That is, a corroded layer of PbO.sub.2 (lead dioxide) may be produced on the surface of the positive collector due to anodic oxidation by repeating charge and discharge cycles after assembling the battery. Although there is no problem since this PbO.sub.2 layer exists as PbO.sub.2 layer in the repeating cycles of usual charge and discharge under only the discharge condition, Pb used as the positive collector metal may be ionized to become Pb.sup.++ ions if the battery is allowed to stand for a long period of the time under the condition, and Pb of PbO.sub.2 layer serving as the corroded layer may become Pb.sup.++ ions similarly. The Pb.sup.++ ions may be bonded with SO.sub.4.sup.-- ions present in an electrolyte to produce an inactive PbSO.sub.4 layer.
In order to avoid such a phenomenon, it has been known (Japanese Published Unexamined Patent Application No. 56-91568) that a positive plate in a lead acid battery is composed of a positive active material and a positive grid in which the positive grid is buried in the internal portion of the positive active material and the outer surface of the positive active material is strongly pressed to prevent unwanted expansion thereof. However, the disadvantage described will not be sufficiently eliminated.
On the one hand, in the battery of this kind, the electrolyte may take part in a battery reaction as shown in the following relation. ##STR1## According to the reaction, it will be apparent that the capacity of the battery of this kind is controlled by the capacity of the negative and positive plates, and the amount of electrolyte.
In order to suppress that the PbO.sub.2 layer of the positive collector surface is changed to the inactive PbSO.sub.4 layer under the discharge storage condition, the inventors have found the electrolyte control type battery structure, that is, the structure in which the battery capacity is controlled by the amount of the electrolyte, and have energetically investigated the same with the result that the present invention has been accomplished.